1. Field of the Invention
The present invention generally relates to an etching method.
2. Description of the Related Art
With the growing miniaturization of etching patterns, precision of the dimensions of patterns formed by etching is becoming an important technical issue. In particular, when the aspect ratio of an etched pattern increases, the dimensions of the etched pattern is prone to degradation. In this respect, PCT Japanese Translation Patent Publication No. 2003-506866 discloses a technique for reducing critical dimension (CD) microloading, which refers to a degradation in the precision of dimensions of a pattern and a decrease in the etch rate as the aspect ratio of the pattern being formed increases.
Also, in view of the miniaturization of patterns, a technique is known for shrinking the critical dimensions (CD) of an etching pattern to reduce the dimensions of a pattern to be etched. In the next generation, pattern miniaturization is expected to progress further, and as such, controlling the shrinkage of the vertical and horizontal CD of a pattern upon shrinking the CD may be important. Normally, the vertical to horizontal CD shrink ratio upon shrinking the CD of a pattern is preferably controlled to be 1:1.
However, in the case of shrinking an oval hole pattern, for example, the long diameter of the hole pattern normally shrinks by a greater amount compared to the short diameter, and it is difficult to control the long diameter to short diameter CD shrink ratio to 1:1.